The present invention relates to a collision-avoidance device for aircraft, notably for avoiding collisions with the ground. It can be applied notably to airliners. More generally, it can be applied to all aircraft that, in the course of their flight, come far too close to the ground, when they are in the vicinity of mountains for example, or have to maneuver in sectors of air space where they are a source of danger or are themselves in danger, in prohibited zones for example.
There are known devices for the avoidance of collisions between the ground and aircraft. These devices are characterized chiefly by the use of radio altimeters, computers giving the barometric height from measurements of pressure and temperature, and navigation means such as an inertial unit or a system of flight management. The principle of these devices lies in the use of an altimetrical height, taken with reference to the ground, and in the use of the variations of the radioaltimetrical or barometrical height. The latter height is used notably because of its higher precision for great heights as compared with the variation in altimetrical height. These distances from the ground are compared with threshold values that themselves depend on the values of heights and on the configuration of the aircraft, depending on whether its undercarriage or flaps are extended for example. When the parameters measured, namely the heights and variations of heights as a function of time notably, exceed the threshold values, an alarm is sent to the crew. However, such devices have the drawback of giving measurements that are far too late with respect to the progress of the aircraft, hence the drawback of generating alarms that come too late, preventing crews from reacting in time. Such devices are therefore liable not to prevent collisions. This fact may arise notably in the event of a sudden upward turn in the relief when the aircraft is moving towards the side of a steep mountain for example. Another drawback of known devices is the fact that they generate unwarranted alarms. These alarms may occur notably when the aircraft are flying over low-altitude mountains with a good safety height but where the upward turns in the relief, albeit harmless, give rise to these false alarms. These false alarms seriously reduce the credibility of these anticollision devices.
Improvements have been made to these devices, notably by introducing data bases by which the value of the thresholds to be taken into account can be modulated as a function of the geographical position of the aircraft. These improvements are liable to diminish the false alarms. However, they necessitate data bases adapted to each type of terrain. Continuing along the lines of this last-mentioned approach, it is possible to envisage having a digital model of the terrain that would make it possible to have permanent knowledge, as a function of its position, of the nature of the relief towards which the aircraft is flying. Nonetheless, the use of such a model calls for a data base that describes the relief with sufficient precision and that therefore requires larger-sized memories. In addition to this drawback, a data base such as this needs exchange procedures and updatings, and this fact complicates its use. The large number of information elements stored furthermore implies non-negligible risks of error.
The aim of the invention is to overcome the above-mentioned drawbacks, notably by eliminating the hazards related to variations in relief and by determining the position of the aircraft no longer with respect to the ground but with respect to known safety altitudes.